This invention relates generally to structural support members of the open web type, such as trusses or joists and, more particularly, to such support members of adjustable length which are mounted on end supports such as walls by means of mounting brackets. The open web structural support member of the present invention is provided with an adjustable connector means including an apertured chord plate for connecting the mounting bracket to the end of the upper chord member in an incrementally adjustable manner in order to adjust the length of the support member between a plurality of different, predetermined length settings. The structural support member also includes an adjustable link means for linking the mounting bracket to the end of a web member positioned at the end of the structural support member to form an end web assembly. The link means has an incremental adjustment means for adjusting the length of such end web assembly in fixed increments between a plurality of different, predetermined web length settings corresponding to the length adjustments of the support member. This incremental adjustment has the advantage that during field installation of the open web structural support member, the proper length of such support member and the corresponding link setting to give the proper length of the end web member can be more easily selected by the installer to provide a rigid and stable support member.
Previously, it has been proposed in U.S. Pat. No. 3,062,340 of Hunnebeck, issued Nov. 6, 1962, to provide metal girder units of the open web truss type for temporary use which may be adjustable in length by adjusting a telescoping extension of the upper boom or chord in predetermined increments. However, unlike the present invention, the end web member of this prior girder apparatus is not provided with incremental adjustment means, but instead is adjusted in a continuous manner by rotation of a threaded rod so that the ultimate adjusted length of the web member may not be of the proper length to match the adjusted length of the truss. This length mismatch can cause the truss to be loose and unstable so that forces applied thereto may result in failure of the truss at lower loads than it was designed to carry. In addition, the continuous adjustment mechanism is too complicated and impractical because each web length adjustment apparatus of such prior girder truss employed two pairs of telescoping web members which were connected together by bridge elements, such bridge elements being threadedly engaged by the threaded adjustment rod for causing telescoping movement of the web members by screw adjustment of such rod for continuously varying the length of the web member. Also, unlike the present invention, the mounting bracket is not a flush mount and is welded to the boom extension so it cannot be used with a variety of chord member sizes. This extremely complicated and expensive adjustment mechanism is inaccurate because it does not position the web member between a plurality of predetermined length settings, which is avoided by the simple and inexpensive adjustable end web assembly of the present invention.
A similar teaching is shown in a later U.S. Pat. No. 3,209,508 by Hunnebeck, issued Oct. 5, 1965, except that the end web member is adjusted by means of a turnbuckle to provide a continuous length adjustment with its resulting disadvantages, rather than incremental adjustment between predetermined web length settings corresponding to the upper boom or chord length settings to provide a rigid, stable truss.
In addition, Swiss Pat. No. 331,145 of Dreyfuss, issued Aug. 30, 1958, shows an adjustable length metal girder or truss similar to U.S. Pat. No. 3,062,340 of Hunnebeck but, however, employs no adjustable length end web member and does not attach its end web member to the mounting bracket. This causes an undesirable eccentric load to be applied to the truss at the end web connection which is avoided by the present invention.
The open web structural support member of the present invention has the additional advantage that the length of such support member can be easily adjusted in the field, merely by removing a pin from the chord plate, sliding the upper chord member relative to the mounting bracket, and then inserting the pin into a different hole in the chord plate attached to such mounting bracket. A corresponding adjustment of the length of the end web assembly is quickly and easily achieved merely by removing a bolt from an adjustment hole in apertured link members and placing it in another hole. As a result of the incremental adjustment of the length of the structural support member or truss and a corresponding incremental adjustment in the length of the end web member, a rigid and stable structural support member is provided with the present invention and inaccurate length adjustments in the field are avoided.
The present structural support member is of improved versatility because its mounting bracket is secured to the chord plate by a pair of bolts which extend through vertical slots in such chord plate and pass beneath the upper chord member to allow chord members of different height to be employed and to accommodate different length adjustment positions of the chord member. In addition, a fixed link member is provided with a pair of fork arms which extend on opposite sides of the end web member to engage such web member and prevent the link-web assembly from collapsing under compressive loads which may be caused by wind uplifts of the lower chord member.